A superelastic aerogel sensing material and its preparation method and application

Abstract

The present invention discloses a superelastic aerogel sensing material and its preparation method and application. In the present invention, cellulose and lignin are dissolved in an alkali / urea solution, and then a cross-linking agent is added to chemically cross-link them to obtain a cellulose / lignin hydrogel. Thereafter, it is immersed in water for swelling to stretch the gel network, and then directionally frozen by liquid nitrogen and placed in a freeze dryer for freeze drying to obtain a superelastic cellulose / lignin aerogel. Finally, it is successively immersed in a pyrrole / hydrochloric acid solution and a ferric chloride / hydrochloric acid solution for in-situ polymerization loading of pyrrole and then freeze-dried to obtain a superelastic aerogel sensing material. The superelastic aerogel sensor prepared by the present invention has excellent elasticity, mechanical stability, fatigue resistance, conductivity and sensing performance, can accurately identify changes in tiny stress and strain, and can be applied to flexible electronic skin, human active health detection and other fields.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent soft materials, and in particular relates to a superelastic aerogel sensing material and a preparation method and application thereof. Background Art

[0002] With the booming development of artificial intelligence, human-computer interaction, the Internet of Things, and wearable electronics, there is an urgent need for high-performance pressure sensors with ultra-high sensitivity and adjustable mechanical properties. Compared with other types of sensors, piezoresistive sensors composed of elastic substrates and conductive materials have excellent sensitivity, fast response, and signal stability to changes caused by stress / strain, making them ideal candidates for next-generation pressure sensors. Lightweight aerogels with adjustable microporous structures, low density, high porosity, and high surface area are ideal substrates for the development of high-performance piezoresistive sensors. However, aerogel-based sensors generally suffer from insufficient substrate elasticity and limited contact resistance changes, resulting in reduced sensitivity, restricted detection range, and prolonged response time.

[0003] Biomass aerogels, third-generation aerogels, offer advantages such as abundant precursors, low cost, a rich variety of functional groups, ease of modification, and biodegradability. They are widely used in thermal insulation, oil-water separation, and sensor substrates. However, biomass aerogels generally suffer from poor mechanical properties, low structural strength, and low elasticity, which limit their widespread application. Within the field of biomass-based aerogel research, cellulose-based aerogels have become a hot topic due to their exceptional properties. Cellulose, a linear polymer composed of β-glucose linked by β-1,4-glycosidic bonds, possesses abundant oxygen-containing functional groups, making it an ideal aerogel precursor. Fu Danning of South China University of Technology has disclosed a nanocellulose-based superelastic, highly conductive, and multifunctional aerogel, as well as its preparation method and application (CN115368622B). This method uses chitosan (CS) to enhance the structural strength of cellulose nanofiber (CNF) aerogels, resulting in a superelastic, highly conductive, and multifunctional aerogel. Although this aerogel exhibits excellent sensing performance, the preparation process of its raw material, CNF, is complex and costly, and CS has limited effect on the elasticity of CNF aerogels. Chen et al. (Advanced Functional Materials 2020, 30, 1910292) introduced lignin into cellulose nanofiber aerogels to enhance their network strength, maintaining their gel network structure during carbonization. The resulting highly elastic carbon aerogel can be used for stress / strain sensing, but the complex CNF preparation process and high energy consumption of the carbonization process result in low sensitivity and poor elasticity of the assembled sensor. Shi Zhuqun of Wuhan University of Technology disclosed a nanocellulose / Ti3C2T~X composite aerogel, its preparation method, and its application (CN114588846A). This aerogel exhibits excellent high compressive elasticity and electrical conductivity. However, the Ti3C2T~X is complex to prepare and has weak interaction with the aerogel. During multiple cycles, the Ti3C2T~X easily falls off, resulting in unstable signals.

[0004] Lignin is one of the most abundant aromatic biomacromolecules in nature, possessing a unique three-dimensional, rigid molecular structure composed of multiple benzene rings. Furthermore, multiple functional groups, such as phenolic hydroxyl groups, alcoholic hydroxyl groups, and carboxyl groups, are embedded within lignin's three-dimensional structure, making it an ideal green crosslinker. Lignin's highly rigid structure, combined with its unique three-dimensional multifunctionality, makes it an ideal structural reinforcement for cellulose aerogels, helping to enhance their mechanical properties and stability while maintaining their environmentally friendly properties.

[0005] Generally speaking, aerogels composed of flexible polymers exhibit good flexibility, but due to the lack of reinforcement from rigid molecular segments, their elasticity is usually unsatisfactory. In contrast, aerogels composed of rigid polymers, while possessing excellent mechanical strength, are often accompanied by high brittleness, which also limits their elasticity. On the other hand, aerogels with large interlayer distances have better elasticity, but they are usually unable to establish effective conductive pathways under low pressure, resulting in problems such as low sensitivity, high detection limits, and long response times. For example, Zhang et al. (Small 2023, 2310038) introduced conductive carbon black into cellulose submicron fiber aerogels to construct highly elastic conductive aerogels for stress sensing. However, the large interlayer distance of the aerogel and the poor dispersion of carbon black in the gel network resulted in low sensitivity of the aerogel. Wang et al. (Carbohydrate Polymers 270, 2021, 118414) combined aramid and nanocellulose to form aerogels and then loaded them with polypyrrole to create conductive aerogels. However, the aerogels had large pore spacing and poor dispersion of the conductive active material, limiting their sensitivity and detection range. Furthermore, too small an interlayer spacing can easily lead to agglomeration of the conductive polymer, reducing the sensitivity of the aerogel sensor. For example, Wu et al. (ACS Applied Polymer Materials 2023, 5, 3938−3948) introduced PEDOT:PSS into a cellulose nanofiber aerogel to construct a conductive cellulose aerogel. While this aerogel exhibited good signal stability, its small interlayer spacing and uneven pore structure resulted in low sensing sensitivity. Therefore, the preparation of high-performance aerogel sensor materials remains challenging. Summary of the Invention

[0006] In order to solve the problems of poor elasticity, low sensitivity, poor signal stability and long response time of traditional piezoresistive aerogels, the primary purpose of the present invention is to provide a method for preparing a superelastic aerogel sensing material.

[0007] This invention uses cellulose as a flexible biomacromolecule and lignin as a rigid biomacromolecule as gel precursors. Through the design of molecular segment microstructures and pore structure microstructures, a "flexible and rigid" superelastic lignin / cellulose aerogel is prepared. Furthermore, by loading the aerogel with a conductive active substance to enhance its conductive network structure, an aerogel with superelasticity, high sensitivity, rapid responsiveness, low hysteresis, a wide detection range, and high signal stability is produced. This solves the problems of poor elasticity, low conductive sensitivity, unstable signal transmission, slow response speed, and narrow detection range that cellulose biomass aerogels often face when used as sensors. This aerogel is expected to replace petroleum-based aerogel sensing materials, reducing the cost and increasing the efficiency of aerogel sensor materials.

[0008] Another object of the present invention is to provide a superelastic aerogel sensing material prepared by the above preparation method.

[0009] Another object of the present invention is to provide an application of the above-mentioned superelastic aerogel sensing material.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing a superelastic aerogel sensing material comprises the following steps:

[0012] (1) Cellulose and lignin are added to a urea / alkali mixed solution. After fully dissolving, a cross-linking agent is added to obtain a lignin / cellulose hydrogel (LCEH) through chemical cross-linking.

[0013] (2) immersing the lignin / cellulose hydrogel in water to allow it to swell;

[0014] (3) Directional freezing of the swollen lignin / cellulose hydrogel and freeze-drying to obtain a directionally frozen lignin / cellulose composite aerogel (DF-LCEA);

[0015] (4) The directional frozen lignin / cellulose composite aerogel was first immersed in a pyrrole (Py) / acid mixed solution, then immersed in a ferric chloride / acid mixed solution to induce pyrrole in situ polymerization, and finally freeze-dried to obtain a superelastic conductive lignin / cellulose aerogel (DF-LCEA@PPy);

[0016] (5) Silane was deposited on the superelastic conductive lignin / cellulose aerogel by thermal chemical vapor deposition to obtain a hydrophobic superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0017] Preferably, the cellulose in step (1) is at least one of hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose and hydroxypropyl cellulose.

[0018] Preferably, the lignin in step (1) is at least one of alkali lignin, lignin sulfonate, enzymatic lignin and solvent-based lignin.

[0019] Preferably, the base in step (1) is at least one of sodium hydroxide and potassium hydroxide.

[0020] Preferably, the cross-linking agent in step (1) is at least one of epichlorohydrin, N,N-methylenebisacrylamide and glutaraldehyde.

[0021] Preferably, the mass ratio of cellulose to lignin in step (1) is (1-4): (1-5); more preferably 3: (3-5).

[0022] Preferably, in the urea / alkali mixed solution of step (1), the mass ratio of urea to alkali is (5-15): (5-10), and the total mass concentration of the urea / alkali mixed solution is 15-25%; more preferably, the mass ratio of urea to alkali is (9-14): (5-10).

[0023] Preferably, the concentration of the cross-linking agent in step (1) in the system of step (1) is 3 to 15 wt%, that is, the percentage of the cross-linking agent in the total mass of lignin, cellulose, urea / alkali mixed solution and cross-linking agent is 3 to 15%.

[0024] Preferably, the ratio of the cellulose to the urea / alkali mixed solution in step (1) is (1-4) g:100 mL; more preferably (2-4) g:100 mL.

[0025] Preferably, the swelling time in step (2) is 6 to 48 hours, more preferably 6 to 24 hours.

[0026] Preferably, the directional freezing method in step (3) is a liquid nitrogen-assisted directional freezing method, specifically placing the swollen lignin / cellulose hydrogel on a copper plate immersed in liquid nitrogen for directional freezing.

[0027] Preferably, the freeze-drying temperature in step (3) is -50 to -90°C, the pressure is 1 to 10 Pa, and the freeze-drying time is 36 to 48 hours.

[0028] Preferably, the concentration of pyrrole in the pyrrole (Py) / acid mixed solution in step (4) is 0.1 to 2 wt%, more preferably 0.5 to 2 wt%, and most preferably 1 to 2 wt%; the soaking time is 10 minutes to 12 hours, more preferably 10 minutes to 2 hours, and most preferably 30 to 60 minutes; and the acid is one of 0.1 to 1 mol / L hydrochloric acid and 0.1 to 1 mol / L sulfuric acid, and most preferably 0.1 to 1 mol / L hydrochloric acid.

[0029] The pyrrole (Py) / acid mixed solution in step (4) is obtained by adding pyrrole to an acid solution and mixing; the ferric chloride / acid mixed solution is obtained by adding ferric chloride to an acid solution and mixing.

[0030] Preferably, the concentration of ferric chloride in the ferric chloride / acid mixed solution in step (4) is 0.1 to 3 mol / L, more preferably 0.5 to 3 mol / L, and most preferably 0.5 to 2.5 mol / L; the soaking time is 0.5 to 12 hours, more preferably 0.5 to 6 hours; and the acid is one of 0.1 to 1 mol / L hydrochloric acid and 0.1 to 1 mol / L sulfuric acid, and most preferably 0.1 to 1 mol / L hydrochloric acid.

[0031] Preferably, the temperature of the ferric chloride / acid mixed solution in step (4) is -5 to 5°C.

[0032] Preferably, the freeze drying in step (4) refers to first freezing at -30 to -18°C for 12 to 48 hours and then freeze drying at -50 to -90°C and 1 to 10 Pa for 36 to 52 hours.

[0033] Preferably, the thermal chemical vapor deposition method in step (5) is: placing the superelastic conductive lignin / cellulose aerogel and silane in the same container, heating, and depositing the silane on the superelastic conductive lignin / cellulose aerogel.

[0034] More preferably, the silane is at least one of methyltrimethoxysilane and methyltrichlorosilane, more preferably methyltrimethoxysilane.

[0035] More preferably, the ratio of the silane to the superelastic conductive lignin / cellulose aerogel is 0.5-2 mL: 0.1-2 g; the heating temperature is 50-80° C., more preferably 60-70° C.; and the heating time is 2-24 hours, more preferably 3-12 hours.

[0036] The superelastic aerogel sensing material is prepared by the above preparation method.

[0037] Application of the above-mentioned superelastic aerogel sensing material.

[0038] Preferably, the application is application in stress sensors and strain sensors.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] 1. The superelastic aerogel sensing material provided by the present invention has a height recovery rate of more than 99% after 100 cycles under 50% strain, a maximum stress retention rate of more than 97%, and an energy loss rate of less than 57% in the first cycle.

[0041] 2. The superelastic aerogel sensing material provided by the present invention has a wide detection limit. As a strain sensor, its detection range is 0.01% strain to 74% strain, and as a stress sensor, its detection range is 4.6 Pa to 30.0 kPa.

[0042] 3. The superelastic aerogel sensing material provided by the present invention has extremely high sensitivity. As a strain sensor, its sensitivity factor can reach 3364, and its linear correlation coefficient is 0.9977; as a stress sensor, its sensitivity can reach 160.34kPa -1 , and its linear correlation coefficient is 0.9971.

[0043] 4. The superelastic aerogel sensing material provided by the present invention has an extremely fast response time, with a compression response time of 9 to 11 ms and a rebound response time of 38 to 50 ms.

[0044] 5. The superelastic aerogel sensing material provided by the present invention has excellent cyclic signal stability. In 1000 cycle experiments under 15% strain, its signal retention rate is higher than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a scanning electron microscope image of the cross section of the aerogel prepared in Example 1.

[0046] Figure 2 This is a scanning electron microscope image of the longitudinal section of the aerogel prepared in Example 1.

[0047] Figure 3 is the pore wall thickness of the aerogel prepared in Example 1.

[0048] Figure 4 The results of the maximum stress retention rate and the energy loss rate of the first cycle in the cyclic compression test of the aerogels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5 and Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, and Example 9 are summarized.

[0049] Figure 5 This is the height recovery rate of the aerogel prepared in Example 1 under different compressive strains.

[0050] Figure 6 The maximum stress retention rate and the first-cycle energy loss rate of the aerogel prepared in Example 1 after 100 cycles at 50% strain.

[0051] Figure 7 This is a sensitivity test of the aerogels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8 and Example 9.

[0052] Figure 8 This is a diagram showing the resistivity change of the aerogel prepared in Example 1 under different dynamic strains.

[0053] Figure 9 This is the signal stability of the aerogel prepared in Example 1 under different stress application speeds.

[0054] Figure 10 The sensitivity of the aerogel prepared in Example 1 as a stress sensor.

[0055] Figure 11The sensitivity of the aerogel prepared in Example 1 as a strain sensor.

[0056] Figure 12 This is the sensing response speed of the aerogel prepared in Example 1.

[0057] Figure 13 This is the sensing lag time of the aerogel prepared in Example 1.

[0058] Figure 14 This is the cyclic signal stability of the aerogel prepared in Example 1. DETAILED DESCRIPTION

[0059] The present invention will be described in further detail below with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

[0060] In the examples of the present invention, if the specific conditions are not specified, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. All raw materials and reagents used without specifying the manufacturer are conventional products that can be purchased from the market.

[0061] Example 1

[0062] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.1 mL of epichlorohydrin to the above solution, stir for 150 seconds, pour into a cube-shaped mold and let it stand to completely gel.

[0063] (2) The prepared hydrogel was immersed in deionized water for 24 hours to allow it to fully swell.

[0064] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying to prepare aerogel.

[0065] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0066] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0067] Example 2

[0068] (1) Add 0.3 g of carboxymethyl cellulose and 0.3 g of lignin sulfonate to 10 mL of 6 / 13 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.3 mL of epichlorohydrin to the above solution, stir for 120 seconds, pour into a cube-shaped mold and let it stand to completely gel.

[0069] (2) The hydrogel prepared above was immersed in deionized water for 36 hours to allow it to fully swell.

[0070] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying for 36 hours to prepare aerogel.

[0071] (4) The above aerogel was immersed in a 2 wt% pyrrole (Py) / 0.5 mol / L sulfuric acid mixed solution for 10 min, and then the above aerogel adsorbed with Py was immersed in a 1.0 mol / L ferric chloride / 0.5 mol / L sulfuric acid mixed solution at 0°C for 12 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours. It was then placed in a -58°C, 4Pa freeze dryer and freeze-dried for 52 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0072] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrichlorosilane (TMCS) and heated in a forced air oven at 50 °C for 24 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0073] Example 3

[0074] (1) Add 0.2 g of hydroxyethyl cellulose and 0.2 g of alkali lignin to 10 mL of a 10 / 9 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.5 mL of epichlorohydrin to the above solution, stir for 100 seconds, and pour into a cube-shaped mold and let it stand to completely gel.

[0075] (2) The prepared hydrogel was immersed in deionized water for 48 hours to allow it to fully swell.

[0076] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying to prepare aerogel.

[0077] (4) The above aerogel was immersed in a 0.5 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 20 min, and then the above aerogel adsorbed with Py was immersed in a -5°C 1.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution for 3 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours. It was then placed in a -58°C, 4 Pa ​​freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0078] (5) The PPy-loaded aerogel was placed in a desiccator containing 1.5 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 50 °C for 6 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0079] Example 4

[0080] (1) Add 0.1 g of hydroxypropyl cellulose and 0.1 g of solvent-based lignin to 10 mL of 5 / 14 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 0.5 mL of epichlorohydrin to the above solution, stir for 120 seconds, pour into a cube-shaped mold and let it stand to completely gel.

[0081] (2) The hydrogel prepared above was immersed in deionized water for 12 hours to allow it to fully swell.

[0082] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -90°C and 4 Pa ​​for freeze drying for 40 hours to prepare aerogel.

[0083] (4) The above aerogel was immersed in a 1.5wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 40 min, and then the above aerogel adsorbed with Py was immersed in a 2 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0℃ for 0.5 h. The DF-LCEA loaded with polypyrrole (PPy) was placed in a -18℃ refrigerator and frozen for 24 hours, and then placed in a -58℃, 4Pa freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0084] (5) The PPy-loaded aerogel was placed in a desiccator containing 2 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 60 °C for 1 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0085] Example 5

[0086] (1) Add 0.3 g of hydroxyethyl cellulose and 0.5 g of alkali lignin to 10 mL of 5 / 14 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 0.7 mL of epichlorohydrin to the above solution, stir for 200 seconds, and pour into a cube-shaped mold and let it stand to completely gel.

[0087] (2) The hydrogel prepared above was immersed in deionized water for 6 hours to allow it to fully swell.

[0088] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying for 42 hours to obtain superelastic aerogel.

[0089] (4) The above aerogel was immersed in a 2 wt% pyrrole (Py) / 0.5 mol / hydrochloric acid mixed solution for 50 min, and then the above aerogel adsorbed with Py was immersed in a 2.5 mol / L ferric chloride / 0.5 mol / hydrochloric acid mixed solution at 0°C for 1.5 hours. Then, the DF-LCEA loaded with polypyrrole (PPy) was placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0090] (5) The PPy-loaded aerogel was placed in a desiccator containing 1.5 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 60 °C for 2 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0091] Example 6

[0092] (1) Add 0.4 g of hydroxypropyl methylcellulose and 0.4 g of alkali lignin to 10 mL of 8 / 11 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 0.9 mL of epichlorohydrin to the above solution, stir for 200 seconds, and pour into a cube-shaped mold and let it stand to completely gel.

[0093] (2) The prepared hydrogel was immersed in deionized water for 32 hours to allow it to fully swell.

[0094] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying for 48 hours to obtain superelastic aerogel.

[0095] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 60 min, and then the above aerogel adsorbed with Py was immersed in a 3.0 mol / L ferric chloride / 0.5 mol / hydrochloric acid mixed solution at 0°C for 3 hours. Then, the DF-LCEA loaded with polypyrrole (PPy) was placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4 Pa ​​freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0096] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 80 °C for 3 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0097] Example 7

[0098] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of a 10 / 9 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then, add 1.3 mL of epichlorohydrin to the above solution, stir for 150 seconds, pour into a cube-shaped mold, and let it stand until it is completely gelled.

[0099] (2) The prepared hydrogel was immersed in deionized water for 6 hours to allow it to fully swell.

[0100] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying for 45 hours to obtain superelastic aerogel.

[0101] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 120 min, and then the above aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 9 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0102] (5) The PPy-loaded aerogel was placed in a desiccator containing 1.5 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 65 °C for 24 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0103] Example 8

[0104] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.1 mL of 0.1 g / mL N,N-methylenebisacrylamide to the above solution, stir for 100 seconds, and pour into a cube-shaped mold and let it stand to completely gel.

[0105] (2) The prepared hydrogel was immersed in deionized water for 24 hours to allow it to fully swell.

[0106] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying to prepare aerogel.

[0107] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0108] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0109] Example 9

[0110] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of 6 / 13 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 0.5 mL of glutaraldehyde to the above solution, stir for 30 seconds, pour into a cube-shaped mold and let it stand to completely gel.

[0111] (2) The prepared hydrogel was immersed in deionized water for 24 hours to allow it to fully swell.

[0112] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying to prepare aerogel.

[0113] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 5°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours to obtain a superelastic conductive lignin / cellulose composite aerogel.

[0114] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0115] Comparative Example 1

[0116] (1) Add 0.4 g of hydroxyethyl cellulose to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.1 mL of epichlorohydrin to the above solution, stir for 150 seconds, pour into a cube-shaped mold and let it stand until it is completely gelled.

[0117] (2) The prepared hydrogel was immersed in deionized water for 24 hours to allow it to fully swell.

[0118] (3) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying to prepare aerogel.

[0119] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours for freeze drying to obtain a conductive cellulose aerogel.

[0120] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-conductive cellulose aerogel sensing material (S-DF-CEA@PPy).

[0121] Comparative Example 2

[0122] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.1 mL of epichlorohydrin to the above solution, stir for 150 seconds, pour into a cube-shaped mold and let it stand to completely gel.

[0123] (2) The prepared hydrogel was immersed in deionized water for 24 hours to allow it to fully swell.

[0124] (3) The swollen hydrogel was placed in a -18°C refrigerator for 24 hours, and then freeze-dried in a freeze dryer at -58°C and 4 Pa ​​for 48 hours to prepare an aerogel.

[0125] (4) The above aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours for freeze drying to obtain a conductive cellulose aerogel.

[0126] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-conductive cellulose aerogel sensing material (S-DF-CEA@PPy).

[0127] Comparative Example 3

[0128] (1) 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin were added to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and magnetically stirred until completely dissolved. The solution was then poured into a cubic mold. Liquid nitrogen was used as a cold source. The swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen. The aerogel was then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying for 48 hours to prepare aerogel.

[0129] (2) The above-mentioned aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above-mentioned aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours for freeze drying to obtain a conductive cellulose aerogel.

[0130] (3) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-conductive cellulose aerogel sensing material (S-DF-CEA@PPy).

[0131] Comparative Example 4

[0132] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then add 1.1 mL of epichlorohydrin to the above solution, stir for 150 seconds, pour into a cube-shaped mold and let it stand to completely gel.

[0133] (2) Using liquid nitrogen as a cold source, the hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen, and then placed in a freeze dryer at -58°C and 4 Pa ​​for freeze drying for 48 hours to prepare aerogel.

[0134] (3) The above-mentioned aerogel was immersed in a 1 wt% pyrrole (Py) / 0.5 mol / L hydrochloric acid mixed solution for 30 min, and then the above-mentioned aerogel adsorbed with Py was immersed in a 0.5 mol / L ferric chloride / 0.5 mol / L hydrochloric acid mixed solution at 0°C for 6 hours. The DF-LCEA loaded with polypyrrole (PPy) was then placed in a -18°C refrigerator and frozen for 24 hours, and then placed in a -58°C, 4Pa freeze dryer for 48 hours for freeze drying to obtain a conductive cellulose aerogel.

[0135] (4) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-conductive cellulose aerogel sensing material (S-DF-CEA@PPy).

[0136] Comparative Example 5

[0137] (1) Add 0.4 g of hydroxyethyl cellulose and 0.4 g of alkali lignin to 10 mL of 7 / 12 / 81 wt% sodium hydroxide / urea / water solution and stir magnetically until completely dissolved. Then, add 1 ml of pyrrole and 0.05 g of ferric chloride to the above solution.

[0138] (2) After the above solution is stirred evenly, add 1.1 mL of epichlorohydrin to the sol, stir for 150 seconds, and then pour it into a cube-shaped mold and let it stand until it is completely gelled.

[0139] (3) The prepared hydrogel was immersed in deionized water for 24 hours to allow it to fully swell.

[0140] (4) Using liquid nitrogen as a cold source, the swollen hydrogel was placed on a copper plate immersed in liquid nitrogen for directional freezing until it was completely frozen. It was then placed in a -18°C refrigerator for 24 hours and then placed in a -58°C, 4 Pa ​​freeze dryer for 48 hours to produce aerogel.

[0141] (5) The PPy-loaded aerogel was placed in a desiccator containing 1 mL of methyltrimethoxysilane (MTMS) and heated in a forced air oven at 70 °C for 12 h to deposit MTMS on DF-LCEA@PPy, thereby obtaining a hydrophobic-superelastic aerogel sensing material (S-DF-LCEA@PPy).

[0142] Test Method

[0143] 1. Compression modulus and maximum stress were measured using a Universele testing machine. The compression test was conducted at a temperature of 25°C and a relative humidity of 40% at a speed of 100 mm·min. -1 The rates were carried out at strains of 40% and 50%, respectively. The maximum stress was directly obtained from the stress-strain curve, and the Young's modulus of the aerogel was calculated from the slope of the linear elastic region on the stress-strain curve. The maximum stress retention rate (MSR) and energy loss rate (ELR) of the aerogel were calculated based on the stress-strain curve. MSR=S L / S0×100%, where S0 is the maximum stress of the first compression cycle; S L is the maximum stress in the last compression cycle. ELR = (W1-W2) / W1×100%, where W1 represents the loading work and W2 represents the unloading work.

[0144] 2. Pressure Sensing Performance Testing: Conductive silver paste and copper foil were applied to both ends of the aerogel to create a piezoresistive pressure sensor. A Keithley 2100 was used to measure the real-time resistance change under various stresses and strains. Sensitivity reflects the sensor's response characteristics and is calculated as S = (∆R / R0) / ∆P, where ∆R is the change in aerogel resistance during compression, R0 is the initial resistance before compression, and ∆P represents the change in applied pressure. When used as a strain sensor, sensitivity is quantified using the sensitivity factor (GF), defined as GF = (∆R / R0) / ε, where ε represents the compressive strain of the aerogel.

[0145] Figure 1 (a) is a scanning electron microscope image of the cross section of Example 1, showing a three-dimensional interconnected honeycomb-like uniform pore structure with an average pore diameter of 44.73±10.78 μm. Figure 1Middle (b) is a scanning electron microscope image of the cross section of Comparative Example 2, showing a disordered macroporous structure with an average pore size of 185.21±128.63 μm. Figure 1 (c) is a cross-sectional SEM image of Comparative Example 4, showing a non-porous / closed-pore structure with an average pore size of 185.21±128.63μm. Figure 1 (a) and Figure 1 (b) shows that the aerogel pore structure constructed by liquid nitrogen assisted-directional freezing method with liquid nitrogen as the cold source is more uniform and the pore size is smaller, which indicates that the gel network of the aerogel prepared by liquid nitrogen assisted-directional freezing method is more uniform. Figure 1 (a) and Figure 1 (c) shows that appropriate swelling time can make the gel network fully swell, increase the uniformity of the gel network and improve the porosity.

[0146] Figure 2 This is a scanning electron microscope image of the longitudinal section of Example 1, showing an oriented vertical porous structure.

[0147] Figure 3 Schematic diagram of the pore wall of Example 1, wherein the average pore wall thickness is 0.52 μm.

[0148] Figure 4 The results of the maximum stress retention rate and the energy loss rate of the first cycle in the cyclic compression test of the aerogels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5 and Examples 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8 and Example 9 are summarized. Figure 4 It can be seen that the introduction of lignin can effectively enhance the elasticity of aerogel, and its maximum stress retention rate is increased from 52.14% to 99.09%, and the first cycle energy loss rate is reduced from 78.42% to 50.21%. Figures 1 to 4 From the data analysis, it can be clearly observed that the oriented porous structure prepared by the directional freezing method has a significant effect on enhancing the elasticity of the aerogel. Specifically, this structural optimization significantly increases the maximum stress retention rate of the aerogel from 68.79% to 99.09%. At the same time, its energy loss rate in the first cycle is significantly reduced from 70.24% to 55.21%. These results show that the directional freezing method plays an important role in improving the elasticity and cyclic stability of the aerogel. From Comparative Example 3 and Example 1 and Figure 4It can be seen that the introduction of epichlorohydrin can effectively enhance the crosslinking degree of the gel system, thereby improving the elasticity of the aerogel network, increasing its maximum stress retention rate from 48.66% to 99.09%, and reducing the first cycle energy loss rate to 55.21%. Figure 4 The data show that the swelling process plays a key role in improving the elasticity of aerogels. The experimental results show that the maximum stress retention rate of the aerogels after swelling treatment is significantly improved, from 86.24% to 99.09%. In addition, the energy loss rate of the first cycle is also improved, from 61.11% to 55.21%. These data fully demonstrate the significant effect of the swelling process in enhancing the elasticity of aerogels and reducing energy loss. The enhancement of aerogel elasticity may be due to the fact that the swelling process fully stretches the gel network, increases the porosity of the aerogel, and reduces the local force concentration during compression. Furthermore, from Example 1 and Comparative Example 5 and Figure 4 It can be seen that the order of adding ferric chloride has a significant impact on the mechanical strength of the aerogel. Under alkaline conditions, ferric chloride will react with sodium hydroxide to form ferric hydroxide, thereby destroying the uniformity of the gel system, causing its maximum stress retention rate to drop sharply and its energy loss rate to increase sharply. From Examples 1, 8, and 9, it can be seen that epichlorohydrin, N,N-methylenebisacrylamide, and glutaraldehyde can all be used as cross-linking agents to prepare highly elastic lignin / cellulose aerogels. Among them, the aerogel prepared with epichlorohydrin as the cross-linking agent has the best elasticity.

[0149] Figure 5 is the height recovery rate of the aerogel prepared in Example 1 within a strain range of 10% to 90%. As can be seen from the figure, the height recovery rate of the aerogel prepared in Example 1 exceeds 90% within a wide strain range of 10% to 80%, indicating that the aerogel prepared in Example 1 has excellent elastic recovery properties.

[0150] Figure 6 The maximum stress retention rate and first-cycle energy loss rate of the aerogel prepared in Example 1 after 100 cycles at 50% strain are shown in the figure. As can be seen from the figure, after 100 cycles at 50% strain, the maximum stress retention rate of the aerogel prepared in Example 1 reaches 99.09%, with almost no stress decay. In addition, its energy loss rate is 55.21%, which further proves that the prepared aerogel has excellent elastic recovery properties and excellent fatigue resistance.

[0151] Figure 7Sensitivity tests were conducted on aerogels prepared in Comparative Examples 1, 2, 3, and 4, as well as Examples 1, 2, 3, 4, 5, 6, 7, 8, and 9. Comparative Examples 1 and 1 demonstrate that the introduction of lignin to create a three-dimensional porous structure effectively improves sensitivity, increasing it from GF = 415 to GF = 1306. Furthermore, Examples 1 and 2 demonstrate that the uniformly oriented small pore structure created by liquid nitrogen-assisted directional freezing is more conducive to pyrrole loading and the creation of more conductive contact points than the disordered large pore structure created by conventional refrigerator freezing. Therefore, the sensitivity of the aerogel constructed by directional freezing was 3.28 times higher than that of the aerogel constructed by conventional refrigerator freezing (from GF = 305 to GF = 1306). Furthermore, by comparing Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Example 7, it can be seen that the immersion time of pyrrole has a crucial influence on the sensitivity of the aerogel. As the immersion time of pyrrole increases, the sensitivity of the aerogel first increases and then decreases, and reaches a maximum value when the immersion time is 30 minutes. This is because the degree of polymerization of pyrrole increases with the increase of immersion time, and when the immersion time exceeds 30 minutes, pyrrole agglomerates, resulting in a decrease in the sensitivity of the aerogel. From Comparative Example 3 and Example 1 and Figure 7 It can be seen that the introduction of epichlorohydrin can effectively improve the sensitivity of the prepared aerogel sensor, increasing it from GF=121 to GF=1306. This is because the addition of epichlorohydrin increases the crosslinking degree of the gel system, increases the porosity, and thus increases the change in contact resistance. Figure 7 It can be seen that the swelling process has a significant effect on improving the sensitivity of aerogel sensors. Specifically, the swelling treatment allows the gel network structure to be fully expanded and the porosity to increase, which increases the loading amount of pyrrole and increases the change in contact resistance. Therefore, the sensitivity of the aerogel sensor after swelling treatment is significantly improved from GF=86 to GF=1306. This result shows that the swelling process plays a key role in enhancing the performance of aerogel sensors. It can be seen from Examples 1, 8 and 9 that epichlorohydrin, N,N-methylenebisacrylamide and glutaraldehyde can be used as cross-linking agents to prepare highly elastic lignin / cellulose aerogels. Among them, the aerogel prepared with epichlorohydrin as the cross-linking agent has the best sensitivity.

[0152] Figure 8 The resistivity change diagram of the aerogel prepared in Example 1 under different dynamic strains. Figure 8 It can be seen that the resistance change (ΔR / R0) of the aerogel prepared in Example 1 increases proportionally with the applied pressure. Figure 8It can be seen that the aerogel prepared in Example 1 can stably and effectively distinguish 0.01% strain to 5% strain, which demonstrates the excellent low-strain detection performance of the aerogel prepared in Example 1.

[0153] Figure 9 This is the signal stability of the aerogel prepared in Example 1 under different stress application speeds. Figure 9 The aerogels prepared in Example 1 were shown to be -1 , 100 mm•min -1 , 150 mm•min -1 , 200 mm•min -1 , 250mm•min -1 The resistivity change is kept stable at a constant speed, that is, the fluctuation of the peak resistivity change (ΔR / R0) is almost negligible, and the signal waveform remains consistent.

[0154] Figure 10 The sensitivity of the aerogel prepared in Example 1 as a stress sensor. As can be seen from the figure, the aerogel prepared in Example 1 shows excellent linear sensitivity in the range of 0 to 300 Pa, and its maximum value can reach 160.93 kPa. -1 In addition, the pressure resolution of the aerogel prepared in Example 1 can reach 4.6 Pa, which has an extremely high pressure resolution and can accurately identify the pressure magnitude.

[0155] Figure 11 Figure 1 shows the sensitivity of the aerogel prepared in Example 1 as a strain sensor. As can be seen from the figure, the aerogel prepared in Example 1 exhibits excellent linear sensitivity within the range of 0.01% to 0.19%, with a maximum value of GF = 3364. Furthermore, the pressure resolution of the aerogel prepared in Example 1 can reach 0.01% strain, demonstrating extremely high strain resolution and the ability to accurately identify strain magnitudes.

[0156] Figure 12 This is the sensing response speed of the aerogel prepared in Example 1. As can be seen from the figure, the compression response speed of the aerogel prepared in Example 1 is 11 ms, and the rebound response speed is 38 ms, which shows that the aerogel prepared in Example 1 has a fast pressure response speed and can quickly respond to and identify pressure signals.

[0157] Figure 13 Figure 1 shows the response lag time of the aerogel prepared in Example 1 at different stress application rates (15% strain). As can be seen from the figure, the fitted lines for the actual and theoretical response times of the aerogel prepared in Example 1 almost overlap, with a slope close to 1 and a linear correlation coefficient of 0.9996.

[0158] Figure 14The cyclic signal stability of the aerogel prepared in Example 1 is shown in the figure. As can be seen from the figure, the aerogel prepared in Example 1 retained 90% of its initial value after 1000 cycles at 15% strain, demonstrating extremely high signal stability. This is attributed to the excellent elasticity imparted by the oriented porous structure combined with the unique rigid / flexible molecular segment microstructure.

[0159] Table 1

[0160]

[0161] Table 1 shows the resistance and conductivity of the aerogels prepared in Example 1 and Comparative Example 5. Analysis of the data in Table 1 shows that the preparation order of DF-LCEA aerogel and the polymerization loading order of polypyrrole have a significant effect on its conductive properties. The preferential synthesis of DF-LCEA aerogel can pre-form a uniform pore structure, providing sufficient loading area for pyrrole, so that pyrrole can be in-situ loaded on the pore wall of the aerogel, and then a uniformly distributed conductive network is constructed in the gel network. On the contrary, if pyrrole and ferric chloride are directly introduced during the gel synthesis process, ferric chloride will react with sodium hydroxide to generate ferric hydroxide precipitate, which not only consumes ferric chloride as an oxidant and initiator, but also hinders pyrrole from forming an effective conductive path in the gel network. Therefore, the choice of preparation order is crucial for the conductive properties of aerogel.

[0162] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a superelastic aerogel sensing material, characterized in that: The following steps are involved: (1) Adding cellulose and lignin to a urea / alkali mixed solution, after fully dissolving, adding a cross-linking agent, and forming a lignin / cellulose hydrogel through chemical cross-linking; (2) immersing the lignin / cellulose hydrogel in water to allow it to swell; (3) Directional freezing and shaping of the swollen lignin / cellulose hydrogel, followed by freeze drying, to obtain a directionally frozen lignin / cellulose composite aerogel; (4) The directionally frozen lignin / cellulose composite aerogel was first immersed in a pyrrole / acid mixed solution, then immersed in a ferric chloride / acid mixed solution to induce pyrrole in situ polymerization, and finally freeze-dried to obtain a superelastic conductive lignin / cellulose aerogel; The mass ratio of cellulose to lignin in step (1) is (1-4): (1-5); The cross-linking agent in step (1) is at least one of epichlorohydrin, N,N-methylenebisacrylamide and glutaraldehyde; The concentration of pyrrole in the pyrrole / acid mixed solution in step (4) is 0.1 to 2 wt %, and the soaking time is 10 minutes to 12 hours; The concentration of ferric chloride in the ferric chloride / acid mixed solution in step (4) is 0.1 to 3 mol / L, and the soaking time is 0.5 to 12 hours.

2. The method for preparing a superelastic aerogel sensing material according to claim 1, characterized in that: The method further includes the following steps: (5) depositing silane on the superelastic conductive lignin / cellulose aerogel by a thermal chemical vapor deposition method to impart hydrophobicity to the material, thereby obtaining a hydrophobic superelastic aerogel sensing material.

3. The method for preparing a superelastic aerogel sensing material according to claim 1, characterized in that: The cellulose in step (1) is at least one of hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose and hydroxypropyl cellulose; The lignin in step (1) is at least one of alkali lignin, lignin sulfonate, enzymatic lignin and solvent-based lignin; The concentration of the cross-linking agent in the step (1) system is 3 to 15 wt%.

4. The method for preparing a superelastic aerogel sensing material according to claim 1, characterized in that: The base in step (1) is at least one of sodium hydroxide and potassium hydroxide; In the urea / alkali mixed solution of step (1), the mass ratio of urea to alkali is (5-15):(5-10), and the total mass concentration of the urea / alkali mixed solution is 15-25%; The ratio of the cellulose to the urea / alkali mixed solution in step (1) is (1-4) g:100 mL.

5. The method for preparing a superelastic aerogel sensing material according to claim 1, characterized in that: The swelling time in step (2) is 6 to 48 hours; The directional freezing method in step (3) is a liquid nitrogen-assisted directional freezing method, specifically placing the swollen lignin / cellulose hydrogel on a copper plate immersed in liquid nitrogen for directional freezing.

6. The method for preparing a superelastic aerogel sensing material according to claim 1, characterized in that: The pyrrole / acid mixed solution in step (4) is obtained by adding pyrrole to an acid solution and mixing, and the ferric chloride / acid mixed solution is obtained by adding ferric chloride to an acid solution and mixing, and the acid solution is one of a 0.1-1 mol / L hydrochloric acid solution and a 0.1-1 mol / L sulfuric acid solution; The temperature of the ferric chloride / acid mixed solution in step (4) is -5 to 5°C; The freeze drying in step (4) refers to first freezing at -30 to -18°C for 12 to 48 hours and then freeze drying at -50 to -90°C and 1 to 10 Pa for 36 to 52 hours.

7. The method for preparing a superelastic aerogel sensing material according to claim 1, characterized in that: The mass ratio of cellulose to lignin in step (1) is 4:(3-5); The ratio of the cellulose to the urea / alkali mixed solution in step (1) is (2-4) g:100 mL; The swelling time in step (2) is 6 to 24 hours; The concentration of pyrrole in the pyrrole / acid mixed solution in step (4) is 0.5 to 2 wt %; the soaking time is 10 minutes to 2 hours; The concentration of ferric chloride in the ferric chloride / acid mixed solution in step (4) is 0.5 to 3 mol / L, and the soaking time is 0.5 to 6 hours.

8. The method for preparing a superelastic aerogel sensing material according to claim 2, characterized in that: The thermal chemical vapor deposition method in step (5) is as follows: placing the superelastic conductive lignin / cellulose aerogel and silane in the same container, heating, and depositing the silane on the superelastic conductive lignin / cellulose aerogel; The silane is at least one of methyltrimethoxysilane and methyltrichlorosilane; The ratio of the silane to the superelastic conductive lignin / cellulose aerogel is 0.5-2 mL: 0.1-2 g; the heating temperature is 50-80° C., and the heating time is 2-24 hours.

9. A superelastic aerogel sensing material prepared by the preparation method according to any one of claims 1 to 8.

10. The use of the superelastic aerogel sensing material according to claim 9, characterized in that: The application is an application in a stress sensor or a strain sensor.

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